1. Field of the Invention
The present invention is in the field of pumps for use in pumping oil from an oil well, and more specifically relates to apparatus for use in a sucker rod pump to adapt it for pumping oils containing sand.
2. The Prior Art
Particles of sand and rock have long been considered to be unwelcome intruders in the pumps used to produce oil. They cause abrasion and friction between the moving parts of the pump, and an accumulation of sand above or below the plunger can prevent motion of the plunger, thereby shutting down the well.
Inventors have long sought to deal with these problems by skillful management of the sand.
In a sucker rod pump, sand causes abrasion of the outer surface of the plunger and the inner surface of the pump barrel within which the plunger reciprocates. This causes wear which increases the clearance between the moving parts, thereby reducing the efficiency of the pump and weakening the parts.
To reduce sand-caused wear on the plunger and pump barrel, pump designers have provided wipers at one or both ends of the plunger. The wipers precede the plunger as it moves, wiping sand from the inner surface of the pump barrel. The wipers are toroidal and may be composed of a variety of materials. Typically, wipers are seated in a circumferential groove on a short cylindrical wiper body of metal. Wiping rings of this type are also called "horizontal wipers" because they are disposed in a plane perpendicular to the axis of the pump barrel, which would be vertical for a vertical well.
Horizontal wiper rings bring with them some unique problems. Sand soon becomes trapped between the upper and lower horizontal wiper rings, thereby increasing the wear inflicted on the plunger and barrel, compared with the wear produced in the absence of the wipers when the circulation of oil between the plunger and barrel tends to carry away the sand rather than to trap it. Further, if too much sand becomes compacted below the lower horizontal ring and above the standing valve, it can stack up the rod string by preventing downward motion of the plunger.
Although horizontal wiping rings are used to this day, other more sophisticated approaches based on the concept of circulating the sand rather than isolating it, have been proposed.
In U.S. Pat. No. 2,635,554 issued Apr. 21, 1953 to Haley, there is described a generally cylindrical shaped plunger having a network of grooves formed in its outer surface. Some of the grooves are disposed in planes perpendicular to and spaced along the axis of the plunger. These horizontal grooves are connected by staggered axially-extending grooves. Radially-extending passages connect the horizontal grooves to the hollow interior of the plunger. In theory, sand precipitating onto the upper end of the plunger will be channeled through the grooves into the bore of the plunger and be produced. There is no provision for wiping the inner surface of the barrel, and sand might collect and pack in the rather small grooves. Ultimately, the excellence of Haley's concept of producing the sand is defeated by the practical difficulty of machining in steel the intricate network of grooves and passages necessary to implement it. As will be seen below, the present invention avoids this practical difficulty and in addition produces a torque that rotates the plunger to distribute the wear more evenly.
In U.S. Pat. No. 2,086,816 issued Jul. 13, 1937 to Mullins there is shown a plunger that has at its upper end a helical ring seated in a helical groove and extending into the clearance space between the plunger and the barrel to serve as a wiper. This device would not be effective in a modern pumping system because the small amount of contact or seal area provided by the helical ring would result in excessive pump slip. Also, the reduced contact area would result in excessive wear of the ring which would reduce its operational life.
In U.S. Pat. No. 2,074,591 issued Mar. 23, 1937 to Rood, there is shown a plunger having helical grooves winding around its external surface. These helical grooves necessarily contain no sealing or wiping rings, but instead are only passages for oil to flow through. A radial passage connects the lower end of each helical groove to a small axial passage inside the plunger that is connected by a miniature check valve to the bore of the plunger. The sand is carried along with some oil through the grooves, passages and check valves to the bore of the plunger and is ultimately produced. In practice it would be extremely expensive to machine the various grooves and passages in a plunger and to install the miniature check valves. Further, the dimensions of these parts must be rather small, and therefore they are susceptible to plugging. Once that has occurred, sand would accumulate in the grooves and accelerate wear.
In U.S. Pat. No. 5,660,534 issued Aug. 26, 1997 to Snow, there is shown the use of helical grooves, located either in the cage or in an attached upper plunger for the purpose of imparting a rotational movement to the plunger about its axis so as to distribute the wear more evenly. The disclosure of this patent is hereby incorporated by reference for the purpose of providing a fuller explanation of the background of the present invention.
Notwithstanding the ingenuity apparent in these earlier patents, a practical and effective solution to the problems associated with sand has not been achieved.